In the past, it has been proposed that it would be possible to use the receiver of the telephone handset as the transducer for the tone ringer, in addition to its normal function as the receiver in the speech network. In particular, R. E. C. Brown U.S. Pat. No. 3,594,515, herein incorporated by reference, contains a general disclosure of such a system, along with a detailed description of other types of tone-ringer circuits. In the Brown proposal, the telephone line-switch contacts are used, in the on-hook state, to connect an incoming low-frequency ringing signal from the central office to a rectifier circuit, which drives an oscillator circuit that in turn drives the handset receiver so as to produce the ringing tones. In the off-hook state, the line-switch contact operate to connect the receiver in the speech network in the normal fashion. Such a proposal, as generally as was described in the Brown patent, filed in 1968, appears to be attractive for various reasons in the development of new types of telephone sets, particularly in the development of electronic telephone sets to be powered solely from the central office. Advantages of such circuitry relates primarily to simplicity, compactness because the circuitry does not require local power, and potental low cost attributable to the dual use of a single receiver component for both functions.
One problem that can be encountered with any attempted use of the Brown suggestion is that, if the handset is removed from the cradle and the line switch is thereafter manually depressed for any reason while the handset receiver is being held close to the user's ear, an incoming ring signal would then activate the receiver so that the user would be "rung in the ear," meaning subjected to what would be unpleasantly loud ringing tones close to the user's ear.